Field of the Invention
The present invention relates to an electric-resistance-welded pipe welding apparatus which bends a metal strip into a cylindrical shape while traveling the metal strip, joins both ends of the metal strip by energizing current through the metal strip with induction heating or direct energization of sliding electrodes, and manufactures an electric-resistance-welded pipe. More particularly, the present invention relates to an electric-resistance-welded pipe welding apparatus capable of welding with high efficiency by effectively eliminating reactive power.
Priority is claimed on Japanese Patent Application No. 2009-214885, filed Sep. 16, 2009 and Japanese Patent Application No. 2009-214887, filed Sep. 16, 2009, the content of which is incorporated herein by reference.
Description of Related Art
As methods for manufacturing a metal pipe, there is a method of manufacturing a seamless pipe by directly making hole into a metal billet, or a method of manufacturing a pipe by extruding a metal, in addition to a method of manufacturing an electric-resistance-welded pipe, a spiral pipe, or the like, in which a metal strip is bent and welded into a pipe shape.
Because of the particularly high productivity and the low cost, electric-resistance-welded pipes have been produced in large quantities. Such electric-resistance-welded pipes are molded into cylindrical shape while the metal strip is traveling, and finally, high frequency current flow is applied to both ends of the metal plate to be joined, so that the temperature of both ends are increased to the melting temperature, and the both end surfaces are press-welded by rolls, resulting in a pipe shape. At this time, as methods for supplying current to both ends of the metal strip, there is a method in which an induction coil is wound so as to surround the outside of the metal and the induction current are directly generated in the metal by making a primary current flow through the induction coil. As another method, there is a method in which metallic electrodes referred to as a “contact tip” are pushed against the ends of the metal strip and current flow directly from a power source to the metal strip. At this time, in many cases, as the current which flows through the conduction coil or the electrodes, high frequency current of 100 to 400 kHz are generally used and a ferromagnetic body referred to as an “impeder” is disposed on or above the inner surface of the pipe. The impeder is used to inhibit the current from flowing around the inner periphery of the metal strip which is just bent into a cylindrical shape.